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The 7.6(5) eV nuclear magnetic-dipole transition in a single 229Th3+ ion may provide the foundation for an optical clock of superb accuracy. A virtual clock transition composed of stretched states within the 5F(5/2) electronic ground level of both nuclear ground and isomeric manifolds is proposed. It is shown to offer unprecedented systematic shift suppression, allowing for clock performance with a total fractional inaccuracy approaching 1×10(-19).

We have produced laser-cooled Wigner crystals of 229 Th 3+ in a linear Paul trap. The magnetic dipole (A) and electric quadrupole (B) hyperfine constants for four low-lying electronic levels and the relative isotope shifts with respect to 232 Th 3+ for three low-lying optical transitions are measured. Using the hyperfine B constants in conjunction with prior atomic structure calculations, a new value of the spectroscopic nuclear electric quadrupole moment Q = 3.11( 16) eb is deduced. These results are a step towards optical excitation of the low-lying isomer level in the 229 Th nucleus.

Entanglement of a 795 nm light polarization qubit and an atomic Rb spin wave qubit for a storage time of 0.1 s is observed by measuring the violation of Bell's inequality (S = 2.65±0.12). Long qubit storage times are achieved by pinning the spin wave in a 1064 nm wavelength optical lattice, with a magic-valued magnetic field superposed to eliminate lattice-induced dephasing. Four-wave mixing in a cold Rb gas is employed to perform light qubit conversion between near infra red (795 nm) and telecom (1367 nm) wavelengths, and after propagation in a telecom fiber, to invert the conversion process. Observed Bell inequality violation (S = 2.66±0.09), at 10 ms storage, confirms preservation of memory/light entanglement through the two stages of light qubit frequency conversion.PACS numbers: 42.50. Dv,03.65.Ud,03.67.Mn Future quantum information processing systems will rely on the ability to generate, distribute and control elementary entanglement processes across continental distances. Besides offering fundamentally more secure ways to communicate, quantum networks may provide the structure for distributed quantum computation. Largescale quantum networks necessarily require mitigation of exponential photon transmission losses, by using compatible quantum memory elements and so-called quantum repeater protocols [1,2]. Compatibility involves storing and retrieving quantum information and transmitting the latter optically, in the case of fiber-based networks, in the telecom wavelength range where absorption is minimized [3]. Unfortunately, typical atomic ground-state electronic transitions suitable for quantum information applications lie outside the telecom window [4][5][6][7][8][9][10][11][12][13]. The entanglement distribution rate of a network also depends critically on the quantum memory lifetime of the storage elements; memory lifetimes of a second or longer may be desirable [1,2,[14][15][16]. The combined attributes of telecom wavelength light and a long-lived quantum memory are therefore essential for fiber-based quantum networks [3].Previously, the entanglement of near-infra red (NIR) light at 795 nm with an atomic spin wave for a 3.3 ms storage period was reported. The memory time was limited by inhomogeneous light shifts in the optical lattice used to eliminate motional dephasing on a sub-ms time-scale [17]. Two orthogonal components associated with the m = ±1 ↔ m ′ = ∓1 coherences of a single mode spin-wave were used to encode the long-lived atomic qubit. Observations of quantum correlations of a long-lived (∼ 0.1 s lifetime) memory with a NIR field, and with a telecom field for 11 ms storage time, were very recently reported [18]. In this work ac Stark decoherence was removed by a new two-photon laser compensation technique.Here we report measurement of entanglement between an atomic spin-wave memory qubit and a telecom field qubit, at a storage time of 10 ms. As in Ref. [18], highefficiency, low-noise wavelength conversion between NIR and telecom fields in an optically-thick, cold Rb gas is at the core of...

A quantum repeater is a system for long-distance quantum communication that employs quantum memory elements to mitigate optical fiber transmission losses. The multiplexed quantum memory (O. A. Collins, S. D. Jenkins, A. Kuzmich, and T. A. B. Kennedy, Phys. Rev. Lett. 98, 060502 (2007)) has been shown theoretically to reduce quantum memory time requirements. We present an initial implementation of a multiplexed quantum memory element in a cold rubidium gas. We show that it is possible to create atomic excitations in arbitrary memory element pairs and demonstrate the violation of Bell's inequality for light fields generated during the write and read processes.